I'll try and do my best to answer this question, in such a way that you'll be able to make some sense out of this, and then apply these guidelines in the future.
The first sentence is an example of the so-called second conditional
If you were a king, what'd your wife be called?
Rightly so, edyta—the OP—said this is an impossible situation. The chances of edyta, whom I presume is a woman, becoming king is even more remote. But the sentence doesn't refer to a past event. Being a king never happened and it never will. The idiomatic phrase If + you + were is expressing an unreal situation, similar to saying: Let's pretend you are a king.
The construction If + subject + past and would + infinitive is often referred to as irrealis, which means that the situation proposed is ‘unreal’ or ‘imaginary’ in the present
See also Present Unreal Conditional
The past verb-form is used to suggest that the situation is probable, or imaginary, or set in a hypothetical future.
Martin Parrott provides this insight:
We use them [type 2 conditional sentences] to refer to or speculate about something that is (or that we perceive to be) impossible or ‘contrary to fact’. This is sometimes presented to learners as ‘very unlikely’. The real point, however, is that at the moment of speaking we see the action or event as being impossible.
Source: Grammar for English Language Teachers
Probable; e.g. “If I were on holiday, I'd go to the beach every day.”
Imaginary; e.g. “If I were a cat, I'd catch mice all day long.”
Or hypothetical future event; e.g. “If I had a car, we would drive down to Mexico.”
The OP's example falls under the category of imaginary, If I were a King. . .
The following sentence is an example of a hypothetical future event
A: What would you do if you needed a haircut?
i. I'd go to the hairdresser's.
ii. I'd cut it myself.
iii. I don't know. Cut it, I guess. Why are you asking?
The so-called ‘third conditional’ is for talking about a hypothetical/imaginary situation in the past (which didn't happen) and its consequence.
If you had worked harder last year, you would have passed your exam
if + past perfect and would have + past participle
See also: Past Unreal Conditional
Thus the sentence (note my correction on the word order)
If you had been king, what would your wife have been called?
Expresses either an imaginary situation in the past that didn't happen, or an event that didn't happen in the past. In both cases, the situation is ‘impossible’ because we cannot change the past.
- Some exclusively use "If it were not for" both for the present and for the past.
- Others use "If it had not been for" for the past, and "If it were not for" for the present.
Consider the attitude (1) as an idiom; take it as-is. In addition to your example [1] (it's OALD), Oxford Dictionary takes this attitude. See its examples in "were it not for".
Those of the case (2) include Longman. The book "Practical English Usage" by Michael Swan, edition y2016, item 244.3 says:
To talk about the past we use If it had not been for.
If it hadn't been for your help, I don't know what I'd have done.
Perhaps usage has changed, but I can't confirm it.
Best Answer
You can say that an if-clause is usually used in conditional sentences, but you cannot say that it is used only in conditional types 1, 2, and 3 sentences. Look at the following sentences that are zero conditional:
If my husband has a cold, I usually catch it.
He gets upset if (=when) I disagree with him.
You also use the if-clause in indirect speech, imperative sentences, etc. as follows:
He asked me if I could come to the meeting.
I asked him if I could help him.
I wonder if he understands what I mean.
Ask him if he can come to the party.
As for the sentence in question, you can use either if or whether, without any difference in meaning:
I have been wondering whether/if it's ok to use weapons or not.